It is common to use metal storage tanks filled with liquid propane under high pressure for various purposes, primarily for domestic purposes, such as cooking and heating. A single manually operable valve disposed at the top of the tank permits selective proportional release of the propane from the tank, thus permitting control of the amount of heat generated by the gas as it combusts.
Such conventional "propane" tanks typically have a fixed volume of about ten litres and require periodic refilling. Such refilling is preferably done when the propane tank is nearly depleted. However, it is quite common to be using the propane tank when it becomes depleted, and is therefore suddenly unusable. Such depletion is common even if the propane tank is equipped with a pressure gauge that indicates the amount of propane remaining in the tank due to imprecision of such gauges. Such unexpected depletion of propane is highly undesirable and is addressed in various manners in the prior art by providing ganged tanks connected in fluid communication one with another. More specifically, "double" propane tanks having a smaller auxiliary tank inside a main tank are known, where the propane inside the smaller auxiliary tank is useable when the propane inside the main tank is depleted.
An example of one such "double" propane tank is found in U.S. Pat. No. 5,429,627 to San entitled Sub-Cylinder for Liquified Petroleum Gas, wherein a cylinder comprises an outer main cylinder and an interiorly mounted sub-cylinder, each cylinder having its own separate independent valve. The outer cylinder is a conventional propane tank and the sub-cylinder is adapted to fit into the threaded aperture that otherwise would receive a pressure gauge. This structure has been proven to be advantageous in terms of ease and familiarity of manufacturing, and also for consumer acceptance as it maintains the appearance and functionality of standard conventional propane tanks.
In use, if the propane has been depleted from the main cylinder of San, the delivery hose can be moved from the main cylinder's valve to the reserve cylinder's valve, thus extending use of the propane tank for a brief period of time, so as to allow, for example, completion of the meal currently being cooked on a propane barbeque or grill. However, such moving of the delivery hose from one valve to the other is extremely inconvenient, especially considering that the flow of propane will be interrupted, thus necessitating the relighting of the apparatus when the propane flow is renewed from the reserve cylinder.
One prior art tank that overcomes the problem of moving the delivery hose from the main tank to the reserve tank is disclosed in U.S. Pat. No. 2,019,004 to Endacott entitled Liquefied Gas Tank, wherein the flow of gas from a large main tank is controlled by a main valve, and the flow of gas from a smaller reserve tank is controlled by a secondary valve through the main valve. However, this arrangement is decidedly disadvantageous in that the external valving mechanisms are undesirably large and cumbersome, thus requiring significant modification to existing main propane tanks in order to add such a valving mechanism, and thereby losing long established consumer acceptance of standardized tanks. Even with a safety ring, such an external valving mechanism is only partially protected and, accordingly, is prone to damage, and for this reason is less safe than is desirable. Further, such a valving mechanism is more expensive than is desirable for domestic-use propane tanks.
It is an object of the present invention to provide a storage tank for storing and selectively dispensing pressurized fuel fluids, particularly propane, which storage tank has a main tank and a reserve tank.
It is an object of the present invention to provide a storage tank for storing and selectively dispensing pressurized combustible fluids, particularly propane, which storage tank has a main tank similar to conventional propane tanks for the purpose of ease and familiarity of manufacturing.
It is an object of the present invention to provide a storage tank for storing and selectively dispensing pressurized combustible fluids, particularly propane, which storage tank employs a single valve for receiving a delivery hose.
It is an object of the present invention to provide a storage tank for storing and selectively dispensing pressurized combustible fluids, particularly propane, wherein the flow of propane is not interrupted when switching from the main tank to the reserve tank.
It is an object of the present invention to provide a storage tank for storing and selectively dispensing pressurized combustible fluids, particularly propane, wherein the external valving mechanism can be used with existing main propane tanks.
It is an object of the present invention to provide a storage tank for storing and selectively dispensing pressurized combustible fluids, particularly propane, wherein the overall valving mechanism is significantly less prone to damage than is the prior art.
It is an object of the present invention to provide a storage tank for storing and selectively dispensing pressurized combustible fluids, particularly propane, wherein the overall valving mechanism is easier and less expensive to manufacture than is the prior art.